1. Field of the Invention
The present invention relates to a radio receiver that receives, in parallel, reception waves respectively reaching branches and a diversity receiver that is incorporated in such a radio receiver.
2. Description of the Related Art
In general, in mobile communication systems, the landforms and planimetries around the radio base station and the mobile station vary every moment as the mobile station (including the vehicle) moves and hence a multipath is formed in a complicated manner and the transmission characteristic of the radio transmission channel vary to a large extent.
Therefore, to maintain desired transmission quality by reducing the degree of fading that is caused by the above-mentioned variation in transmission characteristic, a diversity receiving method is frequently used in mobile stations that access such a mobile communication system.
FIG. 10 shows the configuration of a first conventional diversity receiver.
As shown in FIG. 10, the feeding point of an antenna 91-1 is connected to one contact of a switch 93 and the feeding point of an antenna 91-2 is connected to the other contact of the switch 93. The common contact of the switch 93 is connected to the input of a receiving part 94, and the RSSI output of the receiving part 94 is connected to the control input of the switch 93 via a level comparing part 92. The output of the receiving part 94 is connected to the input of a decision decoding part 97 via an A/D converter 95 and a demodulating part 96 that are cascaded. Transmission information as symbol sequence (described later) appears at the output of the decision decoding part 97.
In the diversity receiver having the above configuration, the switch 94 selects one of reception waves reaching the respective antennas 91-1 and 91-2.
The receiving part 94 generates an intermediate frequency signal by frequency-converting and amplifying the selected reception wave. Further, the receiving part 94 measures the level of the selected reception wave and supplies a measurement result to the level comparing part 92.
Comparing the reception wave level thus supplied with a prescribed lower limit value, the level comparing part 92 requests the switch 93 to select the other reception wave when the reception wave level becomes lower than the lower limit value.
The A/D converter 95 generates, in the intermediate frequency domain or the baseband domain, a digital signal corresponding to the one reception wave by sampling the intermediate frequency signal sequentially at a prescribed frequency and coding resulting individual sampling values.
The demodulating part 96 extracts components (e.g., the amplitude and phase of a subcarrier component) suitable for a modulation scheme that was used for generating the reception wave from the components of the reception wave that are represented by the digital signal.
The decision decoding part 97 sequentially recognizes sequences of those components as symbol positions having maximum likelihood based on the signal space diagram of the above-mentioned modulation scheme and restores transmission information in the form of a symbol sequence that indicates individual symbol positions in time-series order.
It is assumed that the above processing performed by the demodulating part 96 and the decision decoding part 97 is realized as a digital signal processing that is executed by a single DSP (digital signal processor) 98 as indicated by a chain line in FIG. 10.
FIG. 11 shows the configuration of a second conventional diversity receiver. The components in FIG. 11 having the same function and configuration as the corresponding components in FIG. 10 are given the same reference symbols as the latter and will not described.
The diversity receiver shown in FIG. 11 is different from the diversity receiver shown in FIG. 10 in that the level comparing part 92 and the switch 93 are not provided, that the feeding points of the antennas 91-1 and 91-2 are connected to the inputs of A/D converters 102-1 and 102-2 via receiving parts 101-1 and 101-2, respectively, that a demodulating part 103 and a selecting part 104 that are cascaded are provided interstage between the A/D converters 102-1 and 102-2 and the decision decoding part 97, that the two outputs of the demodulating part 103 are connected to the corresponding inputs of a transmission quality monitoring part 105, and that the output of the transmission quality monitoring part 105 is connected to the selection input of the selecting part 104.
In the diversity receiver having the above configuration, the receiving parts 101-1 and 101-2 convert reception waves reaching the antennas 91-1 and 91-2 into intermediate frequency signals, respectively.
The A/D converters 102-1 and 102-2 convert the intermediate frequency signals into digital signals, respectively. The demodulating part 103 extracts, in parallel, sets of components (e.g., the amplitude and phase of a subcarrier component) suitable for a prescribed modulation scheme from the sets of components of the reception waves represented by the respective digital signals. For the sake of simplicity, it is assumed here that the modulation scheme is the xcfx80/4 differential QPSK.
The transmission quality monitoring part 105 determines an error in the signal space (an error with respect to a standard value according to the above-mentioned modulation scheme), symbol by symbol, of each of the sets of components that have been extracted parallel by the demodulating part 103 and correspond to the respective reception waves that reached the antennas 91-1 and 91-2 in parallel, and sequentially computes average values of those errors.
The transmission quality monitoring part 105 outputs binary information indicating a smaller one of the average values.
The selecting part 104 selects one set of components indicated by the binary information from the sets of components that were extracted parallel by the demodulating part 103 as described above and correspond to the respective reception waves that reached the antennas 91-1 and 91-2 in parallel, and supplies the selected components to the decision decoding part 97.
That is, in the diversity receiver shown in FIG. 11, switching diversity is realized by a digital signal processing in the intermediate frequency domain through cooperation between the transmission quality monitoring part 105 and the selecting part 104.
It is assumed that the demodulating part 103, the selecting part 104, the decision decoding part 97, and the transmission quality monitoring part 105 are implemented by a single DSP (digital signal processor) 106 as indicated by a chain line in FIG. 11.
Incidentally, the diversity receiver shown in FIG. 10 is small in hardware scale and power consumption and provides high reliability at a low cost because it has only one receiving part 94 to be mounted.
However, since only one of reception waves reaching the antennas 91-1 and 91-2 in parallel is level-monitored by the level comparing part 92, it is not necessarily the case that the other reception wave has a higher level than the one reception wave.
Therefore, for example, where reception waves are given as a prescribed time slot sequence and switching is made between the contacts of the switch 93 in synchronism with those time slots, the diversity gain is not necessarily kept high when the level of a reception wave received as a certain sets of time slots rapidly decreases. In general, the diversity gain obtained by the diversity receiver shown in FIG. 10 is lower than that obtained in accordance with the post-detection diversity scheme by about 3 dB.
The diversity receiver shown in FIG. 11 provides a higher diversity gain than the diversity receiver shown in FIG. 10 as long as the two receiving parts 101-1 and 101-2 corresponding to the respective antennas 91-1 and 91-2 perform proper band limitation and amplification on reception waves in parallel.
However, having a larger hardware scale and power consumption than the diversity receiver shown in FIG. 10, the diversity receiver shown in FIG. 11 in many cases cannot be applied to, in particular, equipment such as a mobile station of a mobile communication system that should satisfy a severe requirement of power saving as well as other requirements of cost reduction, downsizing, and lightening.
An object of the present invention is to provide a radio receiver and a diversity receiver adaptable to a desired diversity receiving system with flexibility and reliability without largely increasing hardware in scale.
Another object of the invention is to commonly use a single circuit including a.means performing sampling on every reception wave reaching a plurality N of branches and to reliably perform demodulation and decision decoding as a discrete signal processing achieving the sampling theorem.
Another object of the invention is to realize demodulation and decision decoding on a plurality N of reception waves reaching a plurality N of branches as a digital signal processing performed by an information processing device for general purpose or common use.
Another object of the invention is to make reduction in hardware scale more efficient, the closer to the back stage of a branch selecting section the first stage of a circuit commonly used for a plurality N of branches is disposed.
Still another object of the invention is to reduce hardware in scale with more efficiency than in a case where sampling is performed in an intermediate frequency domain.
Yet another object of the invention is to reduce hardware in scale with more efficiency than in a case where sampling is performed in a baseband domain.
A further object of the invention is to apply the basic configuration of the present invention even to a receiving system in which a frequency allocation or a channel allocation and a heterodyne detection scheme adapted to the allocation is prevented from matching due to restraints by cost or the like.
Another object of the invention is to realize a means performing sampling and a circuit for common use including the means as circuits performing signal processing at low speed even when the radio frequency of a reception wave is high.
Another object of the invention is to realize a means performing sampling and a circuit for common use including the means as circuits performing signal processing at low speed even when the radio frequency of a reception wave and the frequency of an intermediate signal generated according to frequency conversion on the reception wave are both high.
Another object of the invention is to perform demodulation and decision decoding with stability and reliability.
Still another object of the invention is to lessen the decrease in noise figure due to either or both of a loss in the feeding paths of each branch and an insertion loss in a means for selecting one of the feeding paths, the larger the gains of an amplifying stage is, as well as to improve the transmission quality.
Yet another object of the invention is to perform receiving processing, according to a switching diversity scheme as a discrete signal processing achieving the sampling theorem, on every reception wave reaching a plurality N of branches, without large increase in hardware size.
A further object of the invention is to reliably select branch selection based on a switching diversity scheme independent of a modulation scheme as long as a symbol position is steadily given.
Another object of the invention is to flexibly adapt to a variety of frequency allocations, channel allocations, modulation schemes, multiple access schemes, and diversity schemes and to obtain high transmission quality at low cost without largely increasing hardware in scale in the receiving end of a radio transmission system.
Another object of the invention is to lighten and downsize a terminal which accesses mobile communication systems and improve the performance, so that the service quality of the mobile communication system can be enhanced.
The aforementioned objects are achieved by a radio receiver in which: reception waves individually reaching a plurality N of branches are cyclically selected at the first frequency equal to a value of the product of the plurality N, a number E equal to or greater than xe2x80x9c2xe2x80x9d, and a symbol frequency; and the instantaneous value of selected reception waves are sampled at a second frequency that is n times the value of the first frequency (n: integer); and a resulting sequence of instantaneous values is split into a plurality N of sequences of instantaneous values individually corresponding to the branches.
In this radio receiver, a single circuit performing the above sampling is commonly used for all the plurality N of branches, and demodulation and decision decoding are reliably performed on every reception waves as a discrete signal processing based on the sampling theorem with accuracy determined by the number E and the ratio of the first frequency to the second frequency.
The aforementioned objects are achieved by a radio receiver in which the split sequences of instantaneous values are individually converted into digital signals.
In this radio receiver, demodulation and decision decoding on the plurality N of reception waves can be realized as a digital signal processing performed by an information processing device for general purpose, common use DSP, or the like.
The aforementioned objects are achieved by a radio receiver in which reception waves individually reaching a plurality N of branches are selected in the radio frequency domain or the intermediate frequency domain.
In this radio receiver, the hardware can be efficiently reduced in scale.
Furthermore, the aforementioned objects are achieved by a radio receiver in which the instantaneous values of reception waves individually reaching the plurality N of branches are sampled in the radio frequency domain.
In this radio receiver, the hardware is reduced in scale more efficiently than in a case where the above-mentioned sampling is performed in the intermediate frequency domain.
The aforementioned objects are also achieved by a radio receiver in which the instantaneous values of reception waves individually reaching the plurality N of branches are sampled in the intermediate frequency domain.
In this radio receiver, the hardware is reduced in scale more efficiently than in a case where the above-mentioned sampling is performed in the baseband domain.
The aforementioned objects are achieved by a radio receiver in which the instantaneous values of reception waves individually reaching the plurality N of branches are sampled in the baseband domain.
In this radio receiver, the present invention can be applied to a receiving system in which frequency allocation or channel allocation and a heterodyne detection scheme are prevented from matching due to restraints by cost or the like.
The aforementioned objects are achieved by a radio receiver in which the instantaneous values of reception waves individually reaching the plurality N of branches are sampled at a frequency lower than the frequency of the carrier signal of the reception waves.
In this radio receiver, a circuit including the means performing the above sampling and commonly used for the plurality N of branches is realized as a circuit performing a signal processing at low speed without use of high-speed devices even when the radio frequency of the reception waves is high.
The above-mentioned objects are achieved by a radio receiver in which the second frequency is equal to or lower than the intermediate frequency.
In this radio receiver, a circuit including the means performing sampling and commonly used for the plurality N of branches can be realized as circuits that perform a signal processing at low speed without use of high-speed devices even when the radio frequency of the reception waves and the frequency of an intermediate frequency signal are both high.
The aforementioned objects are achieved by a radio receiver in which the number E is set at a number that either or both of demodulation and decision decoding are performed with a desired accuracy.
In this radio receiver, the number E may be equal to or greater than a number that the above accuracy is to be the desired value. Therefore, the demodulation and the decision decoding are performed on every means connected in cascade to the plurality N of branches with stability and reliability as long as the speed of processing to be performed is set at a desired small value.
The aforementioned objects are achieved by a radio receiver which comprises a means disposed on the feeding paths of the plurality N of branches and amplifies in parallel the reception waves individually reaching the plurality N of branches.
In the above radio receiver, the larger the gains of the means for the above amplification are, the lower a decrease in noise figure is due to either or both of a loss in the feeding paths of the plurality N of branches and an insertion loss of the means disposed at a subsequent stage of the branches.
The aforementioned objects are achieved by a diversity receiver incorporating the above radio receiver, in which the transmission qualities of reception waves reaching each branch are monitored and a sequence of instantaneous values of a reception wave having the maximum.transmission quality is selected among the sequences of instantaneous values of the reception waves.
In this diversity receiver, a receiving processing according to a switching diversity scheme is performed on each of plurality N of reception waves as a discrete signal processing based on the sampling theorem without largely increasing hardware in size owing to common use of a single circuit including the means performing sampling.
The above objects are achieved by a diversity receiver in which errors from the proper allocation of a symbol position are monitored as the transmission quality.
In this diversity receiver, the branch selection according to the switching diversity scheme is performed with reliability independent of an applied modulation scheme as long as a symbol position is reliably given.
The above-mentioned objects are achieved by a diversity receiver in which the levels of reception waves are monitored as the transmission qualities.
In this diversity receiver, it is possible to compute the transmission qualities and realize switching diversity based on the transmission qualities with simplicity and reliability when a deterioration occurring in accordance with the errors of a phase and a frequency, of the errors in SN ratio occurring in the radio transmission paths of the reception waves individually reaching the plurality N of branches, is negligibly low and a modulation scheme in which all symbol positions in the signal space are located on a complete round whose center is the origin, is applied.
The above-mentioned objects are achieved by a diversity receiver different from the above diversity receiver in that diversity reception is performed by not selecting a branch but combining reception waves individually reaching the branches.
In this diversity receiver, a receiving processing according to a diversity scheme is performed on every reception wave as a discrete signal processing based on the sampling theorem with accuracy determined in accordance with the ratio of the first frequency to the second frequency and the number E without large increase in hardware size owing to commonly using a single circuit including the means that performs sampling.